1. Field of the Invention
A dual compartment anode structure for use in molten carbonate fuel cells. The anode of this invention isolates the molten carbonates electrolyte from contaminated fuel gases and isolates internal reforming catalysts from the molten carbonates electrolyte.
2. Description of the Prior Art
Molten carbonate fuel cells generally comprise a cathode and an anode with their current collectors and an electrolyte tile making contact with both electrodes. Under fuel cell operating conditions, in the range of about 500.degree. to about 700.degree. C., the entire electrolyte tile, the carbonate and the inert support material, forms a two phase structure with liquid carbonate and solid inert support. The electrolyte diaphragms of this type are known as "matrix type" or "paste electrolytes". The electrolyte is in direct contact with the electrodes as is fuel on the anode side and oxidant on the cathode side. Prior art molten carbonate fuel cell anodes are generally porous sintered metallic structures with the molten carbonates electrolyte entering the pores from one side and fuel entering the pores from the adjacent fuel compartment on the other side. Fuel cell performance losses are known to be caused by contamination of the electrolyte by sulfides and chlorides which may be present in impure fuel gases, such as may be obtained from gasification of naturally occurring organic carbonaceous materials, such as coal. See, for example, "Effects of H.sub.2 S on Molten Carbonate Fuel Cells", Robert J. Remick, Final Report, U.S. Department of Energy Contract DE-AC21-83MC20212; DOE/MC/20212-2039 (DE 86010431) May 1986. When using gasification products as fuel, it is desirable to reform the products to enhance the hydrogen content of the fuel by internal reforming within the fuel cell. However, conventional reforming catalysts are known to be poisoned by molten carbonates electrolytes due to active sites being covered by a film of carbonates. See "Development of Internal Reforming Catalysts for the Direct Fuel Cell", Michael Tarjanyi, Lawrence Paetsch, Randolph Bernard, Hossein Ghezel-Ayagh, 1985 Fuel Cell Seminar, Tucson, Ariz., May 19-22, 1985, pgs. 177-181. Additional known problems causing failure in long term endurance of molten carbonate fuel cells also include deformation of the porous anode structure, corrosion of anode side hardware such as current collector, separator plate, and the like, by the molten carbonates electrolyte and electrolyte loss thereby, gas cross-over through the porous anode, and electrolyte loss by anode and cathode dissolution. There have been many attempts to solve one or more of these problems to provide long term fuel cell stability and endurance.
U.S. Pat. No. 3,592,941 teaches a molten carbonate electrolyte fuel cell having a porous cathode separated by the molten carbonates electrolyte from a noble metal membrane anode. The noble membrane anode is porous only to hydrogen and separates the anode fuel compartment from the electrolyte. The U.S. Pat. No. 3,592,941 patent teaches only a single anode compartment and only a metallic membrane anode structure. U.S. Pat. No. 4,404,267 teaches an anode composite for molten carbonate fuel cells wherein copper plated ceramic particles are plated on the face of a porous anode to form a bubble pressure barrier adjacent the electrolyte tile, the pores being sized significantly smaller than the pores of the anode and sized to fill with electrolyte. U.S. Pat. No. 4,448,857 teaches a similar porous structure suitable for a cathode composite. U.S. Pat. No. 4,507,262 teaches a porous sintered copper blank plate affixed to the face of a porous anode wherein the pores are filled with metal oxide by use of an organometallic precurser to provide a bubble pressure barrier. U.S. Pat. No. 3,508,969 teaches a galvanic cell having a metal foil face on a porous fuel electrode to prevent electrolyte contact with the electrode during heating to cell operation temperature followed by consumption of the metal foil at cell operating temperatures. U.S. Pat. No. 2,901,524 teaches transfer of anode reaction products to the cathode inlet stream exterior to a fuel cell.